Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, occipital nerve stimulators to treat chronic headaches, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc.
FIGS. 1A and 1B show an Implantable Pulse Generator (IPG) 100, which includes a biocompatible case 30 formed of titanium, for example. The case 30 usually holds the circuitry and power source or battery necessary for the IPG to function. The IPG 100 is coupled to electrodes 106 via one or more electrode leads (two such leads 102a and 102b are shown), such that the electrodes 106 form an electrode array 110. The electrodes 106 are carried on a flexible body 108, which also houses the individual signal wires 112a-112p, coupled to each electrode. The signal wires 112a-112p are connected to the IPG 100 by way of an interface 115, which may be any suitable device that allows the leads 102 (or a lead extension, not shown) to be removably connected to the IPG 100. Interface 115 may comprise, for example, an electro-mechanical connector arrangement including lead connectors 38a and 38b configured to mate with corresponding connectors on the leads. In the illustrated embodiment, there are eight electrodes on lead 102a, labeled E1-E8, and eight electrodes on lead 102b, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary.
As shown in FIG. 2, an IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as microprocessors, integrated circuits, and capacitors, mounted to the PCB 16. Ultimately, the electronic circuitry performs a therapeutic function, such as neurostimulation. A feedthrough assembly 24 routes the various electrode signals from the electronic substrate assembly 14 to the lead connectors 38a, 38b, which are in turn coupled to the leads 102 (see FIGS. 1A and 1B). The IPG 100 further comprises a header connector 36, which, among other things, houses the lead connectors 38a, 38b. The IPG 100 can further include a telemetry antenna or coil (not shown) for receipt and transmission of data to an external device such as a portable or hand-held or clinician programmer (not shown), which can be mounted within the header connector 36. Alternately, in some embodiments, charging coil 18 may be utilized as both a charging coil and a telemetry coil. The IPG 100 usually also includes a power source, and in particular a rechargeable battery 26.
Also shown in FIG. 2 is an external charger 12 that is used to recharge the battery 26 in the IPG 100, which is explained in further detail below. The external charger 12 itself needs power to operate, and therefore may include its own battery 70, which may also be a battery that is rechargeable using a plug-in-the-wall charging cradle or power cord connection, much like a cellular telephone. Alternatively, the external charger 12 may lack a battery and instead draw its power directly from being plugged into a wall outlet.
The external charger 12 can contain one or more printed circuit boards 72, 74, which contain the circuitry 76 needed to implement its functionality. In one embodiment, and as shown in FIG. 2, most of the circuitry 76 can be located on an orthogonal circuit board 74, which reduces interference and heating that might be produced by the charging coil 17, as is further explained in U.S. Patent Publ. No. 20080027500. The external charger 12 also consists of a case or housing 15, typically formed of a hard plastic, which may be divided into top and bottom portions 15a and 15b connected at junction 13. The case 15 can be hand-held, or body-worn, or portable. Clamps 19 may be utilized to hold the circuit boards 72 and 74 in place mechanically, but other means may be used as well.
To wirelessly transmit energy 29 between the external charger 12 and the IPG 100, and as shown in FIG. 2, the charger 12 typically includes an alternating current (AC) coil 17 that supplies energy 29 in the form of a magnetic field to a similar charging coil 18 located in or on the IPG 100 via inductive coupling. In this regard, the coil 17 within the external charger 12 is wrapped in a plane that preferably lies substantially parallel to the plane of the coil 18 within the IPG 100. Such a means of inductive energy transfer can occur transcutaneously, i.e., through the patient's tissue 25. The energy 29 received by the IPG's coil 18 can be rectified and used to recharge battery 26 in the IPG 100, which in turn powers the electronic circuitry that runs the IPG 100. Alternatively, the energy 29 received can be used to directly power the IPG's electronic circuitry, which may lack a battery altogether. The provision of energy 29 may be controlled via the use of a simple user interface comprising, e.g., power on/off button 80 located on the exterior of the case of the external charger. Charger 12's user interface may also contain a single or multiple LED indicator lights to alert the patient of the on/off status of the charger and other relevant charger statuses, as may be desired for a given implementation.
As shown in FIG. 3, external chargers 12 may face a variety of different charging scenarios during use by a patient. Such charging scenarios may involve one or more implantable devices, with such implantable devices being implanted at varying depths and angles with respect to the charging coil 17 of the external charger 12. To further complicate the charging scenario, the implantable devices may also be located at varying distances from each other in the patient. For example, in scenario 200a shown in FIG. 3, there are two implantable devices, 100a and 100b, located a relatively small distance, D, apart from each other and having charging coils 18 oriented at offset angles of θ and θ′, respectively, with respect to the surface of the patient's skin 25, and hence the charging coil 17 in the external charger 12. In some such scenarios, the power of the charging coil 17 in external charger 12 must be increased due to the inefficiency of power transfer caused by the orientation and/or the depth of the implantable devices.
In other scenarios, such as scenario 200b shown in FIG. 3, there may be a large number of implantable devices, e.g., implantable devices 100c-100g, implanted over a relatively greater distance, D′. Even if the offset angle θ″ with respect to the charging coil 17 is small, it may be more desirable for the patient to use a charging coil 17 with a much larger diameter, e.g., larger than D′, so that all implants may be charged simultaneously without the patient having to worry about moving the external charger.
A system has been proposed for charging an implant using an external controller to which a single external charging coil assembly can be coupled. Typically, an external controller is only used to telemeter data to and from the implant, and does not otherwise contain any means for charging the implant. This approach to implant charging is disclosed in U.S. Patent Publ. No. 20090118796 (“the '796 Publication”).
The inventors believe that further improvements can be made to the versatility and design of external charging systems. The external charger 12 of FIG. 2 may not be sufficiently large or powerful enough for certain implantable device charging scenarios, as already noted. The solution of the '796 Publication requires use of the external controller to charge the implant, even though the external controller is not otherwise needed. Thus, the patient must have their external controller handy in case charging is needed, which is an inconvenience.